The widespread availability of computers and communication devices (e.g. cellular telephones) has generated a rapid increase in the number of data networks. Networking two or more computers together allows the computers to share information, file resources, printers, etc. Connecting two or more computers together to form a network is, in principle, a simple task. The computers are simply connected together using a cable, and the necessary software is installed onto the computers. In network terminology, the cable is the network medium and the computers and printers are the network nodes. Unfortunately, in practice, creating a computer network is often not quite as simple as it sounds.
The electrical signal environment of a network medium typically limits the maximum speed at which data can be transmitted over the medium. The maximum speed is generally limited by the maximum bandwidth available on the medium and the noise (or more precisely, the signal to noise ratio) encountered on the medium. While the bandwidth of the medium is usually quite predictable, the noise (and thus the signal to noise ratio) can be unpredictable. Typical noise sources include motors, switching transients, ElectroMagnetic Interference, and the like. Noise-like sources can also include electrical discontinuities in the medium. Electrical discontinuities such as and connectors, cable bends, impedance variations, and the like, create reflections that interfere with data transmission.
In multi-channel systems, where the medium supports multiple independent channels, the changing characteristics of noise on the line can create situations where data sent on some channels is successfully received at the destination node while data on other channels (bad channels) is lost. Systems that retransmit lost data, that is, data bad channels, can suffer from excess system complexity, cost, and/or slow data throughput due to the overhead and latency associated with setting up the transmitter to retransmit lost data.